NOGALES, Ariz. -- The top Democratic and Republican Senate negotiators on forthcoming immigration-reform legislation toured the Arizona-Mexico border on Wednesday, watching as U.S. authorities apprehended a woman who had scaled a border fence and reiterating their commitment to strengthening security along the international line.

Sen. John McCain, R-Ariz., and Sen. Charles Schumer, D-N.Y., are leading the ongoing bipartisan “Gang of Eight” talks that many hope will result in the introduction of a sweeping bill when the Senate returns to session after a two-week Easter break.

The two veteran lawmakers were joined on the tour, which included a helicopter ride, by two other Gang of Eight members: Sens. Jeff Flake, R-Ariz., and Michael Bennet, D-Colo. The senators have been struggling to come to terms on big issues such as the future flow of foreign workers into the country, but the message from the quartet in southern Arizona was that the bill is moving forward.

Schumer, who is chairman of the Senate Judiciary Committee’s immigration subcommittee, was making his first visit to the border and said his observations will make it easier for him to persuade colleagues about the need for additional border measures.

“What I learned today is we have adequate manpower but not adequate technology,” Schumer said at a noon news conference. “And John has been saying that all along.”

At one point during the border tour, the senators witnessed a woman scaling an 18-foot fence a few yards from the entourage. McCain tweeted about the incident, telling his Twitter audience that the Border Patrol took the woman into custody.

“One of the sad things about all of this is that most of those people who jump over the fence are doing that because they want a better life, and I understand that,” McCain elaborated to reporters later. “So we separate the drug cartels from individuals who are simply trying to cross over so that they can improve their lives, but at the same time, we have to have a legal way of doing that. And we will be setting up legal ways of applying for visas, green cards, etc. Not through a border that is porous, which only favors those who live closest and disfavors those who live further away.”

The senators started their day with a 7 a.m. briefing by the Border Patrol. The group set out for the border from Tucson just before 8 a.m. and wrapped up just before the news conference in Nogales.

Under a framework of principles announced by Schumer and McCain’s group on Jan. 28, the measure would link a pathway to citizenship for the estimated 11 million undocumented immigrants already in the country to enhanced border security. According to the framework, the senators contemplate a commission of governors, attorneys general and other “community leaders living along the Southwest border” to gauge border-security progress, but how much authority the panel would have has never been made clear.

President Barack Obama supports comprehensive immigration reform and has encouraged the bipartisan Senate group, which is racing the calendar. The senators have a limited time to pass immigration legislation before Capitol Hill is overtaken by 2014 midterm politics, which could start taking hold as soon as this fall.

Despite continuing deliberations and “a few little problems to work on,” Schumer said the Gang of Eight is “90 percent there” and “we believe we’ll meet our deadline.” Schumer declined to identify lingering points of contention, saying the senators won’t negotiate in public.

“Senator McCain and Senator Flake had impressed upon our group from the beginning the need to do something further on the border, and this trip certainly strengthens that view,” said Schumer, who had planned to meet later with Arizona Latino leaders. “But there are many other things that we have to do as well. We have to determine the future flow: How do we determine who comes into this country in the future? We have to make sure the system, not only at the border, but internally is tighter, so that employers will not hire people who are not here legally. And we have to provide a path to citizenship for the 11 million who are in the shadows.”

Schumer said he hopes the legislation can stay “revenue neutral,” even though more money will be spent to bolster the border. He said the bill will include new “specific metrics” to measure border-security progress, but wouldn’t go into detail.

“And once the border is secured by specific metrics ... people can become citizens,” he said. The legislation ideally would generate enough revenue to pay for itself through, for example, fees paid by high-tech firms to bring in foreign employees.

Bennet said the nation’s broken immigration system is having “all kinds of negative effects” in his home state of Colorado, mentioning that he has heard concerns from peach growers, cattle ranchers, the immigrant-rights community and school officials.

“Not everybody is going to get everything they want in this bill,” Bennet said. “Not one person is writing this by themselves. But if we can get the kind of bipartisan cooperation that’s been demonstrated by the negotiators in this group of eight, I think we can be successful, and I think we can fix a lot of the issues that ail us.”

The senators’ visit to the border drew reaction from immigration-reform activists.

A group called the Dream Action Coalition countered that the border already is effectively secured.

“We hope that Senator Schumer, who has been calling himself a ‘friend’ to the immigrant and Latino community for many years, stops focusing on what is happening at the southern border and calling for more enforcement,” the group said in a statement. “Instead, we ask for his leadership on the real problem we are facing in this country. The reality is that there are more than 1,000 deportations every day and atrocious family separation that is hurting children, parents and our community as a whole.”

Outside McCain’s Phoenix office, about 30 people gathered as part of an event organized by the Arizona Worker Rights Center to spotlight the abuse of immigrant workers, such as unsafe working conditions and “wage theft,” and call on McCain and Flake to addresses those problems in the legislation.

“If you legalize workers, it will raise wages for all workers,” said Nick de la Puente, of the Arizona Worker Rights Center, a non-profit labor-rights organization. “We need to be in favor of immigration reform, regardless of your immigration status.”

De la Puente said his group has documented more than $2million in unpaid wages over the last four years stemming from 320 cases involving undocumented workers. Unscrupulous employers who exploit undocumented workers lower wages for all workers, including legal immigrants and U.S. citizens, he said.

The protesters also delivered letters to McCain’s staff opposing a guest-worker program, which they said could lead to further exploitation of workers.

De la Puente said he opposes the program unless it allows immigrant workers to move to other jobs and also gives them the option to apply for permanent residency.

Schumer suggested the Arizona visit was particularly rewarding for him. The “amazing tour” let the senators see the often rugged terrain that the Border Patrol must cover, Schumer said, and how the officials use manned and unmanned aircraft and forward operating bases. But he and McCain said there is a need to upgrade technological surveillance capabilities.

“We saw the various different types of fencing, and then we saw that there were lots of areas where a fence wouldn’t be practical,” Schumer said. “It would be hugely expensive to build and not practical. ... Then we saw an urban area like Nogales. And so there’s not one size that fits all.”

McCain said the bipartisan group has “not had any differences on this (border security) issue.”

Overall, there has been progress at the border, McCain said, although he added that automatic spending cuts that recently took effect because of sequestration have made the border “less secure.”

“There has been improvements made, and we are very grateful for the men and women who are doing this very difficult work and we’re proud that we have them defending us,” McCain said. “I am very glad my colleagues came.”

McCain jokingly called the other members of the Gang of Eight — Sens. Dick Durbin, D-Ill.; Lindsey Graham, R-S.C.; Robert Menendez, D-N.J.; and Marco Rubio, R-Fla. — who did not tour the border on Wednesday “jerks.”

He then added that the other four have told him that they, too, would like to inspect the border for themselves in the future.

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